In many instances, GPS may not be available to a navigation user. In hostile conditions, GPS may be jammed or otherwise defeated. In indoor application, GPS has insufficient power to penetrate the walls of buildings.
GPS now provides at least four ranging sources simultaneously which enables instantaneous, three-dimensional positioning. However, GPS has a low-power signal that limits operations indoors or in conditions of heavy jamming. A fundamental advantage of the system described herein is that it simultaneously addresses the limitations of its predecessors, providing a dynamic, three-dimensional, accurate position fixes—even indoors or in the presence of jamming.
The Low Earth Orbiting (LEO) satellite constellations, such as Iridium, have been suggested as offering a precise user time standard allowing navigation without using GPS. Patents have been granted for using the time standard from the LEO satellites for augmenting the functionality of the GPS system include such patents as U.S. Pat. RE 37,256, issued to Cohen, et al. entitled, “System and Method For Generating Precise Position Determinations;” U.S. Pat. No. 5,812,961 issued to Enge, et al. entitled, “Method And Receiver Using A Low Earth Orbiting Satellite Signal To Augment The Global Positioning System;” U.S. Pat. No. 5,944,770 issued to Enge, et al. entitled, “Method And Receiver Using A Low Earth Orbiting Satellite Signal To Augment The Global Positioning System;” and U.S. Pat. No. 6,373,432 issued to Rabinowitz, et al. entitiled “System Using LEO Satellites For Centimeter-Level Navigation. These patents still rely, in large part, upon the GPS system.
The performance of MEMS technology is evolving rapidly and can often be optimized for various applications. MEMS technology has been applied to tuning forks in order to produce accelerometer that resolve acceleration to an extent to allow some navigational use. Inertial-grade mechanical inertial units can also provide a means for inertial navigation. In some applications alternating between GPS navigation and inertial navigation has been used for navigation where GPS access is intermittent. Such systems rely upon the presence of GPS to initially fix a position for subsequent inertial navigation.
What is needed is a low-cost, accessible means for precise navigation that operates independently of GPS.